Throughout the mechanical arts, Universal joints are provided to drivingly connect adjacent ends of pairs of elongate rotary shafts and the like; the longitudinal axes of which are misaligned or are subject to being moved in to and out of axial alignment during intended use and operation of the shafts.
In those situations where; the speed of rotation of a pair of angularly related axes shafts is high; the torsional forces encountered are low; and, the angle of deflection of the shafts is great; gimbo-type Universal joints, sometimes called Cardan joints or Hooke's couplings are most commonly used. Such joints are space-consuming; costly to make and maintain; and, are rather weak.
As a result of the above, in the many instances where gimbo-type joints cannot be advantageously employed and where circumstances otherwise permit, many in the art resort to the adoption and use of ball and socket-type Universal joints that are characterized by elongate female parts with outer ends that are secured to related ends of one of a pair of related shafts and inner ends with longitudinally inwardly opening socket openings defining flat longitudinally inwardly disposed bottoms and pluralities of circumferentially spaced, radially inwardly disposed, longitudinally extending flats. Such joints are next characterized by elongate male parts with outer ends that are secured to related ends of the other shaft of the pair of shafts. The male parts have substantially spherical balls or heads at their other or inner ends. The heads correspond in cross-section with the socket openings in their related female parts. That is, the heads have pluralities of circumferentially spaced, longitudinally extending facets that are laterally straight and that are curved longitudinally about the centers of the heads. The heads of the male parts are slidably engaged in the socket openings of the female parts so that, in theory, the facets on the heads of the male parts establish sliding engagement with the flats in the socket openings in the female parts.
The outer portions of the male parts are smaller in diameter than the heads or the heads are joined with the outer portions of their related male parts by intermediate neck portions of reduced diameter so that the heads are free to turn within their related socket openings and attain desired angular deflection of the parts.
With the above basic ball and socket-type joint structure, it will be apparent that the heads and socket openings cooperate to establish rotary driving engagement between the male and female parts and that the heads can be slidably turned within the socket openings to compensate for or to allow for axial misalignment or angular deflection of the parts.
Ball and socket Universal joints of the character referred to are extremely easy and economical to make and are extremely strong compared with gimbo-type joints such as referred to above.
The principal shortcomings found in ball and socket-type joints of the character referred to above reside in the fact that working clearances occur between the heads and the sockets. If such clearance is not built into the joints, it soon develops as the joints are used. As a result of the noted clearances, the flats and facets in the socket openings and on the heads of the joint parts do not, in fact, establish sliding bearing engagement with each other to establish rotary driving engagement between the parts. Instead, the heads of the male parts turn axially, a short distance, within the socket openings of the female parts so that only those edges on the heads that are defined by the converging side portions of adjacent facets engage the flats in the socket openings when the parts are rotatably driven. Further, due to the convex curvature of the convex edges, they only establish point contact with the flats.
When the male and female parts are axially misaligned and are in rotary driving engagement with each other, the points of contact between the noted edges and flats move or slide back and forth longitudinally relative to each other. That movement results in frictional wear and scuffing of the edges and the flats. Still further, the angle between the leading sides or the flanks of the noted edges (defined by the trailing edge portions of the facets) is extremely small and such that those sides of the edges tend to be urged into tight wedging engagement with the flats and result in wedging forces that tend to lock the parts together and to crush the noted edges at their points of contact with the flats. Finally, the trailing sides or flanks of the edges on the heads are moved from engagement with the flats in their related socket openings and are totally uncontained and unsupported.
As a result of the several above-noted shortcomings in joints of the character here concerned with, there is a great tendency for the edges on the heads of the female parts to be crushed, displaced, scuffed away or otherwise reduced to such an extent that the joints are rendered inoperative. Once reduction of the noted edges has commenced, the rate at which the noted edges are reduced accelerates at a rapid rate.
Another shortcoming found in ordinary ball and socket-type joints of the character referred to above resides in the fact that the turning forces (applied torque) are also turned or deflected within the joints, from the axis of one shaft to the axis of the other shaft. When those forces are deflected, as noted, portions thereof are resolved in what are essentially compressive forces between the edges on the heads of the male part and the flats in the socket openings in the female parts and are frictionally dissipated. The portions of those turning forces dissipated in friction increases exponentially with the increase of angular deflection between the parts.
Still further, the above-noted deflected forces are not deflected uniformly between the several edges and flats as the joints rotate but fluctuate as the parts of the joints rotate so that the greater part of those forces are concentrated on and through the related pairs of edges and flats as they move through that plane on which the shafts are angularly deflected. Thus, the greater part of the subject forces are intermittently concentrated on the one or a pair of related edges and flats that occur at diametrically opposite sides of the parts, on or near the noted plane on which the parts are angularly deflected.
Those forces lost to friction are, as noted above, all too often reach a point where they tend to cramp or freeze-up the joints and render them impractical to use or inoperable. Such cramping of the joints tends to occur and become troublesome when the angle of deflection of the male and female parts exceeds 22.5 degrees. When the forces encountered become sufficient to cause the joints to cramp, as noted above, they are often sufficient to result in the reduction of the edges on the heads of the male parts of the joints as noted above.
Another shortcoming existing in joints of the character referred to above resides in the fluctuation in the velocity of rotation of the two parts. This shortcoming can be and has long been overcome by connecting two joints in series. Such series connected joints are sometimes called compound joints.
Another shortcoming encountered in ball and socket-type joints of the character referred to above resides in the tendency for the male parts to slide out of engagement born within the socket openings in the female parts. The prior art has sought to eliminate this shortcoming by providing radially inwardly projecting stop flanges or equivalent stop means in the open end portions of the socket openings, past which the heads cannot move to become disengaged.
Yet another shortcoming encountered in joints of the character here concerned with is the tendency of the male and female parts to pivot freely relative to each other and in such a manner that the joints are difficult and troublesome to work with. The prior art has overcome this problem by placing axially extending compression springs between the bottoms of the socket openings in the female parts and the inner ends of the heads on the male parts. The springs urge the male parts axially outward into engagement with stop means within the socket openings. This relationship of parts effectively serves to yieldingly maintain the male and female parts against free pivoting relative to each other so that the joints can be easily and conveniently worked with.